Hi Mezteck,
Welcome and I’m glad you found us 
If the only issue with a mattress is that it is too firm and there are no soft spots or sagging in the mattress then a good quality topper can certainly be an effective way to add some additional softness, “comfort” and pressure relief to your sleeping system but the only way to know for certain whether a specific mattress/topper combination is a good “match” for you in terms of comfort, firmness, and PPP is based on your own careful testing or personal experience on the combination. If you can’t test the combination in person then there will always be always some risk and uncertainty involved in adding a topper because the specifics of the mattress itself along with your own body type, sleeping position, and preferences can affect which specific topper would be a suitable choice on any specific mattress.
There is more information about choosing a topper and a link to the better online sources I’m aware of in post #2 here and the topper guidelines it links to which along with a conversation with a reliable and knowledgeable supplier (that can provide you with good information about how their toppers compare to each other or to other toppers they are familiar with that are available on the market) can help you use your sleeping experience as a reference point and guideline to help you choose the type, thickness, and firmness for a topper that has the least possible risk and the best chance for success. A good exchange/return policy can also reduce the risk of an online topper purchase so I would make sure you are comfortable with the options you have available after a purchase just in case the topper you choose doesn’t turn out as well as you hoped for.
If a mattress/topper combination turns out to be a good “match” for you in terms of “comfort”, firmness, and PPP then having a separate topper also has the advantage of being able to replace just the topper without replacing the entire mattress if it softens or breaks down before the upper foam layers in the mattress (which is very likely because the upper layers of a sleeping system tend to soften or break down before the deeper layers) or if your needs or preferences change over time. A suitable topper can also help extend the useful life of the mattress underneath it because it will absorb much of the compression forces that can soften or break down the top layers of the mattress underneath it over time.
The better options or possibilities I’m aware of in and around the Kansas City area (which would include Lees Summit) are listed in post #2 here. There are several places that carry latex mattresses (and/or toppers) that may help give you some reference points for different types and blends of latex in different firmness ranges but I would also keep in mind that a topper (or the top few inches of a mattress) can feel different if the layers and components under the topper (or under the top few inches in the mattress) are different so your testing may not be exactly the same as sleeping on a topper on top of a different mattress.
Phoenix